From the article:
“Family members describe themselves as part of a Mormon community of about 3,000 members, living in their own agricultural community in Mexico.”
So these people chose to live in one of the most violent and dangerous areas of the Western Hemisphere, likely to be “left alone” to practice their unorthodox version of Mormonism as there is a lot of cheap land and privacy in the remote region of Sonora. They likely knew the risk when they settled there. That doesn’t mean they deserved this but the adults should bare some blame for putting their families in a dangerous situation.